In recent years, there have been great improvements in DVD (Digital Versatile Disc), its use has spread widely and is now produced on a mass production scale. An example of a production method of DVD in wide use today, very briefly, includes the steps of: setting a stamper, which has a slit for forming information signals, to a mold for injection molding; forming a disc substrate of 0.6 mm thickness by the injection molding; forming a layer or film of a reflecting layer on a surface on which the slit exists; and, after that, adhering or sticking two disc substrates together by using a light-colored or clear (hereinafter, clear) adhesive. By applying this method, a finished product is obtained. With respect to an apparatus applying such a method in which the DVD is produced by adhering two disc substrates, various structures of production lines have already been proposed (for example, see Japanese Patent Application, First Publication No. 2002-245692).
On the other hand, a disc which is applicable to high-density recording as an information recording medium which can be applied to a next generation high-recording density has been developed. With respect to this disc, applicable to high-density recording, upon recording and reading/playing back, a laser with a short wavelength such as 405 nm is applied from the opposite side of the disc; therefore, it is required to form a light transmission layer which is a thin layer with a 100-μm (0.1-mm) thickness and which is clear on the reflecting layer. Moreover, in a case of a disc which is applicable to high-density recording on two signal layers, it is required to form: another light transmission layer having a second signal layer; a semitransparent reflecting layer; and a clear covering layer, wherein the thickness should be approximately 100 μm including the light transmission layer and the covering layer. Uniformity of thickness of the light transmission layer and the covering layer has great effects upon recording and reading information; therefore, a high level of uniformity is required.
Therefore, a method and an apparatus for forming a light transmission layer with high uniformity, by supplying a radiation-hardening liquid material at a position as close to a center portion of the disc substrate as possible and by conducting spin-coating, are already disclosed (for example, see Japanese Patent No. 3557863 and Japanese Patent Application, First Publication No. 2004-220750). Moreover, if an air bubble is included between the light transmission layer which is clear and inside and the covering layer, there are great effects upon recording and reading the information; therefore, a method and an apparatus, in which a disc substrate with a first signal layer and a printing/transferring disc substrate with a second signal layer are adhered, is already disclosed (for example, see Japanese Patent No. 3302630). A method and an apparatus for reliably and easily peeling, detaching or removing the printing/transferring disc substrate is already disclosed as well (for example, see Japanese Patent Application, First Publication No. 2002-197731).